The present invention relates to an exhaust gas recirculation system, and more particularly to a method and system for controlling an exhaust gas recirculation system system.
There is a growing concern over the long-term effects of Nitrogen Oxides (hereinafter NOx) and Carbon Dioxide (hereinafter “CO2”) and Sulfur Oxides such as, but not limiting of, SO2 and SO3 (hereinafter “SOx”) emissions on the environment. The allowable levels of emissions that may be emitted by a turbomachine, such as a gas turbine, are heavily regulated. Operators of turbomachines desire methods of reducing the levels of NOx, CO2, and SOx emitted.
Exhaust gas recirculation (EGR) generally involves recirculating a portion of the emitted exhaust through an inlet portion of the turbomachine. The exhaust is then mixed with the incoming airflow prior to combustion. The EGR process facilitates the removal and sequestration of concentrated CO2, and may also reduces the NOx and SOx emission levels.
Generally, the EGR process concentrates CO2 in the exhaust stream, and reduces the exhaust stream volume such that CO2 may be more easily sequestered in a downstream process. However, there is a similar impact of concentrating any sulfur contained in the fuel. Sulfur reacts with oxygen to produce SOx in the exhaust stream, which upon recirculation becomes more concentrated. The saturated and cooled exhaust stream is mixed with ambient air, creating an inlet fluid, inside the gas turbine inlet. Here a generated condensate drops out containing sulfuric acid, which may corrode compressor blades if carried downstream into the compressor inlet.
Significant amounts of condensable vapors exist in the exhaust gas stream. These vapors usually contain a variety of constituents such as water, acids, aldehydes, hydrocarbons, sulfur oxides, and chlorine compounds. Left untreated, these constituents will accelerate corrosion and fouling of the internal components if allowed to enter the gas turbine.
There are a few concerns with the currently known EGR systems. Impurities and moisture within the exhaust gas prevent utilizing a simple re-circulating loop to reduce the generation of emissions, such as SOx emissions. Turbine fouling, corrosion, and accelerated wear of internal turbomachine components would result from introducing the exhaust gas directly to an inlet portion of the turbomachine. As a result, the diverted exhaust gas should be treated prior to blending with the inlet air.
For the foregoing reasons, there is a need for a method for controlling an EGR system. The method should reduce the level of the liquid products derived from SOx emissions. The method should seek to maintain a temperature of the inlet fluid above a condensation temperature.